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Simple 50MHz J-Pole Antenna

Simple 50MHz-J-Pole-Antenna (DK7ZB)

The principle of the Wireman-J-Pole:

The picture shows the currents in the antenna. At the both ends of the Lambda/2-section (L1) you have a high impedance (some KOhms) and a low current.

At the other side at the end of the Lambda/4-line (L2) is a maximum of the current (low impedance of about 20 Ohms). The two ends are connected together through the metal of the coax-socket (see next picture below).

At the points XX you can find a 50-Ohm-point for feeding with the coax-cable.

Because the quarterwave-line is symmetrical, you should feed with a lambda/4-choke for a SWR of 1,0 at 50,150 MHz.

The bandwidth for a SWR <1,5 is greater than 1 MHz. The gain and pattern are the same as with a normal vertical dipole, but feeding is much more easier.

For the elevation plot and gain look at the other vertical with a Collins-filter!

Practical mounting of the J-Pole:

This J-Pole is mounted on a fishing rod. The radiator L1 is an isolated copper-wire with a length of 281,5 cm (with not-insulated wire about 1-2% longer!). The quarter-wave matching sector L2 is made with 450-Ohm-Wireman-cable (length 133cm).

The matching cable is tapped 65mm from the shortened bottom (coax-socket) and fed with a coax-choke of 1,00 m RG-174, wound on a plastic tube. This choke will handle 100 Wtts output. For RF-power up to 500 Wtts use RG-58 for the choke.

  Fuente: http://www.qsl.net/dk7zb/6m/50mhz-J-Pole.htm


Para el cáculo de la antena podemos guiarnos del siguiente gráfico.

Es recomendable instalar un choque de RF de 125mm de diámetro construido con 4-6 espiras de cable coaxial.

Hecha la simulación de esta antena con el Programa MMANA GAL nos indica lo siguiente:






Para otras frecuecnias las medidas son

Frecuencia

L1

L2

D1

D2

50 Mhz

282 cm

141 cm

15 cm

9 cm

144 Mhz

98.5 cm

48.5 cm

7,5 cm

8 cm

432 Mhz

33 cm

16 cm

3 cm

4 cm


y para mecanizarla se pueden tomar ideas de estas otras imágnes:

   

FUENTE: http://www.rgetna.org/resource/jpole.htm



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